The selection of jurors, who both the prosecution and defense believe can be objective in the highly publicized case, is expected to take all week.
Prosecutors and defense attorneys are looking for six objective members and four alternates. In Florida, 12 jurors are required only for trials involving capital cases, when the death penalty is being considered.
The first group of 100 potential jurors filled out questionnaires about themselves and their ability to serve on the jury. Zimmerman was present as his defense attorneys and prosecutors introduced themselves to the potential jurors.
Judge Debra Nelson has said she will keep the identities of the selected jurors anonymous but she rejected a defense request to sequester the entire jury pool of 500 residents.
Jury selection will coincide with a continuing hearing to determine whether testimony of voice-recognition experts will be allowed. The experts say they might be able to identify who was screaming on a 911 tape recorded during Zimmerman's confrontation with Martin. So far, the experts have reached mixed conclusions, and defense attorneys don't want them to testify.
Nelson denied a defense request to delay the start of the trial. Defense attorney Mark O'Mara said he needed several more weeks to prepare, blaming prosecutors for a delay in turning over evidence. Specifically, he cited the need to interview an attorney for Martin's family.
Zimmerman, a former neighborhood watch volunteer, is charged with second-degree murder for shooting the unarmed teen as he walked home from a convenience store last February. There is no dispute Zimmerman shot Martin; the defense will have to prove Zimmerman's claim that he acted in self-defense.
If convicted, Zimmerman could get a life sentence.
Debate over whether this is a case of self defense or of racial profiling was expected to spark protests outside the courtroom, though the turnout Monday was less than expected, with just a little more than a dozen protesters showing up. They included relatives of Oscar Grant, a man who was fatally shot by an Oakland, Calif., police officer in 2009, and members of a Communist Party group.
For the past year, Zimmerman has been free on $1 million bond and living in seclusion. It's not clear if he will take the stand, though he has testified in pretrial hearings.
The Associated Press contributed to this report.